JPS5933864B2 - Nuclear fuel assembly support device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear fuel assembly support device that prevents leakage of liquid metal coolant and also prevents floating of nuclear fuel assemblies.

A nuclear fuel assembly houses a number of fuel pins therein and is supported within a reactor vessel.

The fuel pin is configured to bring a coolant such as liquid metal into contact with the fuel pin to perform heat exchange.

Incidentally, the fuel pins in the nuclear fuel assembly are replaced by taking the assembly out of the reactor vessel.

Therefore, the assembly must be supported within the furnace vessel in such a way that it can be easily installed and removed.

However, since a large number of assemblies must be arranged in a non-contact manner within the reactor vessel, if the support condition is uncertain, the assemblies may tilt and the assemblies may come into contact with each other within the reactor vessel.

Therefore, in general, an entrance nozzle is provided at the lower end of the assembly, and this entrance nozzle is inserted from above into a connecting pipe provided in the furnace vessel to support it, and the flow rate is set on each peripheral wall of the connecting pipe and entrance nozzle. Coolant flows into the entrance nozzle through the adjustment hole,
It is designed to use the pressure of the coolant to press the assembly downward to stabilize the support state.

At this time, since the pressure loss between the fuel pin and the entrance nozzle is large, the pressure increases between the connecting pipe and the entrance nozzle, and there is a force that causes the assembly to float, which weakens the force pushing the assembly downward. This has the disadvantage that the support of the assembly becomes unstable.

Furthermore, since the pressure between the connecting pipe and the entrance nozzle is so high, the coolant leaks from a small gap between the upper end of the connecting pipe and the outer circumferential surface of the assembly that abuts this portion.

By the way, since the calorific value of all the aggregates loaded in the furnace vessel is not constant, the flow rate is distributed taking into account the difference in calorific value, so that the temperature at the outlet of each aggregate is constant. I have to.

However, as the floating blades of the aggregates become larger and coolant begins to leak from between the connecting pipe and the entrance nozzle, it becomes difficult to distribute the flow rate to each aggregate, resulting in uneven temperature distribution at the outlet of each aggregate. This may lead to a decrease in thermal efficiency, and may also cause thermal deformation in the outlet section.

The present invention was made in order to eliminate such conventional drawbacks, and its purpose is to provide a nuclear fuel assembly that can prevent coolant leakage with a simple structure and that can reliably support the assembly. An object of the present invention is to provide an aggregate support device.

Hereinafter, details of the present invention will be explained based on embodiments shown in the drawings.

FIG. 1 is a sectional view partially showing the inside of the furnace vessel 1. Inside the furnace vessel 1, an upper support plate 2 and a lower support plate 3 are arranged horizontally.

A low-pressure coolant chamber 4 is formed below the lower support plate 3.

A large number of connecting pipes 5 are vertically provided between the upper and lower support plates 2 and 3, and the low-pressure coolant chamber 4 and the upper part of the upper support plate 2 communicate with each other via these connecting pipes 5. .

Further, a high pressure coolant chamber 6 is formed between the upper and lower support plates 2.3.

The connecting pipe 5 has a flow rate adjustment hole 7 in its peripheral wall, and an entrance nozzle 9 provided at the lower end of the nuclear fuel assembly 8 is inserted from above into the connecting pipe 5. The assembly 8 is then loaded into the furnace vessel 1.

The nuclear fuel assembly 8 accommodates a large number of fuel pins 10 inside, as shown in FIG. An entrance nozzle 9 is provided, and a flow rate adjustment hole 13 is also provided in the peripheral wall of the entrance nozzle 9.

These flow rate adjustment holes 13... are connected to the flow rate adjustment holes T of the connecting pipe 5 when the assembly 8 is loaded in a fixed position.
It is now consistent with...

Further, the lower neutron shield 12 is disposed above the entrance nozzle 9, and the coolant flowing from the flow rate adjustment hole 13 passes through the periphery of the shield 12 and reaches the fuel pin 10. It is supposed to reach.

In the assembly support device configured as described above, the coolant supplied from below the reactor vessel 1 flows into the high pressure coolant chamber 6 from below the low pressure coolant chamber 4, and further flows through the connecting pipe 5 and the entrance nozzle. 9 flow rate adjustment holes γ..., 13...
・Flows into the aggregate 8 through.

The coolant then passes through the periphery of the shield 12, contacts the fuel pins 10, performs a predetermined heat exchange, and further passes through the flow path 11a provided in the upper shield 11 to form the assembly 8. It begins to leak outside.

At this time, the lower surface of the entrance nozzle 9 (low pressure coolant chamber 4
A pressure of P3 is applied to the surface in contact with , and the force that lifts the aggregate 8 is .

The present invention has been made to reduce the size of the floating blade of the nuclear fuel assembly 8, and an embodiment thereof is shown in FIG.

In other words, in FIG.
A diffuser 20 with a protruding inner surface central portion 16 is connected to the diffuser 20, so that the coolant flow path is narrowed down to the lower surface 17 of the entrance nozzle 9, and then extremely narrowed at the center portion 16 of the diffuser 20. The purpose is to gradually expand the coolant to make the flow of coolant downward and to press the lower part 15 of the entrance nozzle against the inner surface of the diffuser 20, thereby preventing the nuclear fuel assembly from floating up.

That is, in FIG. 3, since the pressure of the coolant introduced into the connecting pipe 5 is high, it flows into the low-pressure coolant chamber 4.

This flow path is narrowed from around the opening in the middle of Figure 3 to C (squeezed so that the cross-sectional area of the flow path is the same from the opening to C) to increase the flow velocity.

Thereafter, the diffuser 20 is used to spread the flow gently to reduce fluid resistance as much as possible.

In this case, the static pressure distribution from A to 2 will be as shown in Figure 4.

At this time, the flow velocity is high from the mouth to C, and the dynamic pressure becomes large, so the static pressure P2 becomes small.

The reason why the total pressure distribution (dynamic pressure + static pressure) decreases in 2 is due to frictional pressure loss, etc.

This static pressure P2 can be made considerably smaller than P3.

According to the present invention, the pressure applied to the lower surface of the entrance nozzle 9 is not P3 but P2.

Therefore, the force that pushes the lower surface of the entrance nozzle 9 and causes the nuclear fuel assembly 8 to float is ÷Dte·P2.

Since P3>>P2, the force for floating the assembly 8 is attenuated compared to the conventional device, and the assembly 8 is stably supported at the upper end of the connecting pipe 5.

Therefore, the temperature distribution at the outlet of each assembly 8 can be made uniform without causing the assembly 8 to float during an earthquake and disrupting the flow distribution to each assembly 8. This improves the safety of the reactor and improves thermal efficiency. It is also possible to improve the temperature and prevent thermal deformation at the outlet section.

5 and 6 show another embodiment of the present invention, in which a plurality of circumferential protrusions 21 are provided at the lower part of the entrance nozzle 9.
(Three are provided in FIGS. 5 and 6, but any number may be used as long as it is three or more.) The purpose of this is to prevent the assembly 8 from tilting.

In other words, eccentricity of the diaphragm, the diffuser 20, and the tip of the entrance nozzle 9 is avoided.

As explained above, according to the present invention, a diffuser part is machined in the lower fitting part of the nuclear fuel assembly entrance nozzle and the lower inner surface of the connecting pipe to increase the flow velocity of the coolant, and the low hydrostatic pressure of the diffuser part is Since the force that draws the entrance nozzle downward is generated by the pressure difference between the entrance nozzle internal pressures, it is possible to prevent the nuclear fuel assembly from floating.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged vertical cross-sectional view of the inside of the fast reactor vessel for explaining the present invention, and FIG. 2 shows the state in which the conventional nuclear fuel assembly shown in FIG. 1 is inserted into the connecting pipe. 3 is a sectional view showing the nuclear fuel assembly support device according to the present invention; FIG. 4 is a distribution curve diagram showing the static pressure distribution and dynamic pressure distribution of the coolant in FIG. 3; FIG. 5 is a sectional view partially showing essential parts of another embodiment of the nuclear fuel assembly support device according to the present invention, and FIG. 6 is a sectional view taken in the direction of arrows A and -A in FIG. 1...Furnace vessel, 5...Connecting pipe, 8...
Nuclear fuel assembly, 9 Entrance nozzle, 10 Fuel pin, 12 Neutron shield, 13 Flow rate adjustment hole, 20・・・・・・
・Diffuser (including part of the aperture mechanism), 21...
...protrusion.

Claims (1)

[Claims] 1. A nuclear fuel assembly that accommodates a fuel pin inside, has a neutron shield placed below the fuel pin accommodating part, has an entrance nozzle at the lower end, and has a coolant inlet on the peripheral wall of the entrance nozzle, is installed at the entrance of the nuclear fuel assembly. In a nuclear fuel assembly support device in which a nozzle is inserted from above into a connecting pipe provided in a reactor vessel and supported within the reactor vessel, the lower end of the entrance nozzle is formed into a cone-proof shape, and a A nuclear fuel assembly support device characterized by being provided with a diffuser whose inner surface has a protruding central portion.